The present invention relates to an engine for mounting on a vehicle, primarily a motorcycle or a motor tricycle, and more particularly, to an improvement in the engine casing structure in which the crankcase for housing the crankshaft and the transmission case for housing the vehicle's transmission are formed as an integrated structure.
In such engines of conventional construction, such as, for example, that described in Japanese Utility Model Laid-Open Publication No. 54-27250, a lower opening for permitting the crankshaft and the transmission to be mounted and demounted is formed through the lower end surface of the transmission case and the oil pan is connected to this lower end surface. When the crankshaft is intended to be removed from the crankcase, the transmission must first be removed, causing an impedance in vehicle maintainability.
If, on the other hand, the lower opening of the transmission case in these prior art engines is expanded to a lower end surface of the crankcase so as to provide sufficient space to permit the crankshaft to be removed without interfering with the transmission, the rigidity of the crankcase and the transmission case is disadvantageously reduced.
Also, as best exemplified in Japanese Patent Application No. 58-54233, such prior art engine organizations, in which the engine starting device includes a ring gear driven by a starting motor, that is rotatably supported on the crankshaft and connected thereto by an overrunning clutch, require a stopper member secured to the crankshaft by a bolt, or the like, for preventing detachment of the ring gear from the crankshaft. Such stopper members and fasteners have heretofore been dedicated members that are characterized by a complicated construction.
It is to the amerlioration of these problems, therefore, that the present invention is directed.